import cv2

bgr_img = cv2.imread('statue_small.jpg')

bgra_img = cv2.cvtColor(bgr_img, cv2.COLOR_BGR2BGRA)
b, g, r, a = cv2.split(bgra_img)
a[:, :] = 172
bgra_172 = cv2.merge([b, g, r, a])
a[:, :] = 0
bgra_0 = cv2.merge([b, g, r, a])

cv2.imwrite('source.png', bgr_img)
cv2.imwrite('bgra_0.png', bgra_0)
cv2.imwrite('bgra_172.png', bgra_172)
